FIR Absorption in CdSe Quantum Dot Ensembles

excitation of confined dipolar vibrational modes was studied, both theoretically and experimentally. Spatial quantisation of optical phonons was analysed in the framework of a continuum model, which couples the phonon amplitude to the electrostatic potential via the Fröhlich interaction. The frequencies and oscillator strengths of the dipole-active optical vibration modes are presented cal-culated for a spherical QD, and for the first time for II–VI QDs these quantised modes were observed experimentally. Another effect studied in this work is the influence of the QD concentra-tion on the FIR absorption of their ensemble. It is shown that the dipole–dipole interaction be-comes very important in dense QD ensembles and leads to smearing of the structure in the CdSe phonon band as the QD concentration increases. 1. Introduction The optical properties of semiconductor quantum dot (QD) ensembles in the far-infrared (FIR) spectral region have received much less attention of research-ers compared to those in the visible-to-ultraviolet one. This is despite the fact that FIR spectroscopy can probe confined optical phonons and eventually provide information about the electromagnetic interaction between QDs. Spatial quantisation of optical pho